The invention relates to golf balls and, more particularly, to golf balls having covers that comprise a saturated polyurethane and a UV absorber.
Golf ball covers are formed from a variety of materials, including balata and ionomer resins. Balata is a natural or synthetic trans-polyisoprene rubber. Balata covered balls are favored by the more highly skilled golfers because the softness of the cover allows the player to achieve spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots.
However, balata covered balls are easily damaged, and thus lack the durability required by the average golfer. Accordingly, alternative cover compositions have been developed in an attempt to provide balls with spin rates and a feel approaching those of balata covered balls, while also providing a golf ball with a higher durability and overall distance.
Ionomer resins have, to a large extent, replaced balata as a cover stock material. Chemically, ionomer resins are a copolymer of an olefin and an alpha, beta ethylenically-unsaturated carboxylic acid having 10-90% of the carboxylic acid groups neutralized by a metal ion. See U.S. Pat. No. 3,264,272. Commercially available ionomer resins include, for example, copolymers of ethylene and methacrylic or acrylic acid neutralized with metal salts. These are sold by E.I. DuPont de Nemours and Co. under the trademark SURLYN(copyright) and by the Exxon Corporation under the trademark ESCOR(copyright) and the trademark IOTEK(copyright). These ionomer resins are distinguished by the type of metal ion, the amount of acid, and the degree of neutralization.
U.S. Pat. Nos. 3,454,280, 3,819,768, 4,323,247, 4,526,375, 4,884,814, and 4,911,451 all relate to the use of SURLYN(copyright)-type compositions in golf ball covers. However, while SURLYN(copyright) covered golf balls as described in the preceding patents possess virtually cutproof covers, they have inferior spin and feel properties as compared to balata covered balls.
Polyurethanes have also been recognized as useful materials for golf ball covers since as early as about 1960. U.S. Pat. No. 3,147,324, filed Oct. 20, 1960, is directed to a method of making a golf ball having a polyurethane cover. The curing agents disclosed are diamines, polyols or air moisture. The disclosed polyurethane covered golf balls are durable, while at the same time maintaining the xe2x80x9cfeelxe2x80x9d of a balata ball.
Since 1960, various companies have investigated the usefulness of polyurethane as a golf ball cover material. U.S. Pat. No. 4,123,061 issued Oct. 31, 1978 teaches that a golf ball can be made from a polyurethane prepolymer of polyether and a curing agent, such as a trifunctional polyol, a tetrafunctional polyol or a diamine. U.S. Pat. No. 5,334,673 issued Aug. 2, 1994 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes for forming golf ball covers, and in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent and/or a difunctional glycol.
The first commercially successful polyurethane covered golf ball was the Titleist(copyright) Professional golf ball in 1993. The principal reason for the delay in bringing polyurethane composition golf ball covers on the market was that it was a daunting engineering task to apply a covering of polyurethane composition to a golf ball core to form a golf ball cover having a uniform thickness.
In particular, the difficulty resided in centering a golf ball core in an amount of polyurethane that was sufficiently cured to keep the core centered while at the same time being insufficiently cured so that the cover material could be molded around the core. Resolution of this problem thus enabled production of the aforesaid Professional polyurethane covered golf ball to commence in 1993.
Unlike SURLYN(copyright) covered golf balls, polyurethane golf ball covers can be formulated to possess the soft xe2x80x9cfeelxe2x80x9d of balata covered golf balls. However, golf ball covers made from polyurethane have not, to date, fully matched SURLYN(copyright) golf balls with respect to resilience or the rebound of the golf ball cover, which is a function of the initial velocity of a golf ball after impact with a golf club.
Furthermore, because the polyurethanes used to make the covers of such golf balls contain an aromatic component, e.g., an aromatic diisocyanate, polyol or polyamine, they are susceptible to discoloration upon exposure to light, particularly UV light. To slow down the discoloration, light and UV stabilizers, e.g., TINUVIN(copyright) 770, 765 and 328, are added to these aromatic polymeric materials. However, to further ensure that the covers formed from aromatic polyurethanes do not appear discolored, the covers are painted with white paint and then with a clear coat to maintain the white color of the golf ball. The application of a uniform white pigmented coat to the dimpled surface of the golf ball is a difficult process which adds time and costs to the manufacture of the golf ball. Thus, there remains a need for polyurethane materials which do not discolor and which are suitable for forming a golf ball.
The invention is directed to a golf ball including a core and a cover layer wherein the cover is formed of a polyurethane composition including of a prepolymer comprising a saturated diisocyanate and a curing agent, and a UV absorber.
In one embodiment, the prepolymer further includes an initiated polycaprolactone. Preferably, the initiated polycaprolactone comprises of diethylene glycol-initiated polycaprolactone; 1,4-butanediol-initiated polycaprolactone; 1,6-hexanediol-initiated polycaprolactone; trimethylol propane-initiated polycaprolactone; neopentyl glycol-initiated polycaprolactone; polytetramethylene ether glycol-initiated polycaprolactone; and mixtures thereof.
In another embodiment, the prepolymer further includes polytetramethylene ether glycol; poly(oxypropylene)glycol; polyethylene adipate glycol; polyethylene propylene adipate glycol; polybutylene adipate glycol; polycarbonate glycol; ethylene oxide-capped polyoxypropylene diol; and mixtures thereof. Alternatively, the saturated diisocyanate includes ethylene diisocyanate; propylene-1,2-diisocyanate; tetramethylene-1,4-diisocyanate; 1,6-hexamethylene-diisocyanate; 2,2,4-trimethylhexamethylene diisocyanate; 2,4,4-trimethylhexamethylene diisocyanate; dodecane-1,12-diisocyanate; dicyclohexylmethane diisocyanate; cyclobutane-1,3-diisocyanate; cyclohexane-1,3-diisocyanate; cyclohexane-1,4-diisocyanate; 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane; isophorone diisocyanate; methyl cyclohexylene diisocyanate; triisocyanate of 1,6-hexamethylene-diisocyanate; triisocyanate of 2,2,4-trimethyl-1,6-hexane diisocyanate; 4,4xe2x80x2-dicyclohexylmethane diisocyanate, and mixtures thereof. Preferably, the saturated diisocyanate includes 4,4xe2x80x2-dicyclohexylmethane diisocyanate.
In another embodiment, the curing agent includes 1,4-butanediol; isomers and mixtures of cyclohexyldimethylol; ethylene glycol; diethylene glycol; polytetramethylene ether glycol; propylene glycol; trimethanolpropane; tetra-(2-hydroxypropyl)-ethylenediamine; isomers and mixtures of cyclohexane-bis-(methylamine); triisopropanolamine; 4,4xe2x80x2-dicyclohexylmethane diamine; isomers and mixtures of diaminocyclohexane; 2,2,4-trimethyl-1,6-hexanediamine; 2,4,4-trimethyl-1,6-hexanediamine; diethyleneglycol di-(aminopropyl)ether; 4,4xe2x80x2-bis-(sec-butylamino)-dicyclohexylmethane; 1,2-bis-(sec-butylamino)cyclohexane; 1,4-bis-(sec-butylamino)cyclohexane; isophorone diamine; hexamethylene diamine; propylene diamine; 1-methyl-2,4-cyclohexyl diamine; 1-methyl-2,6-cyclohexyl diamine; ethylene diamine; diethylene triamine; triethylene tetramine; tetraethylene pentamine; 1,3-diaminopropane; dimethylamino propylamine; diethylamino propylamine; imido-bis-propylamine; monoethanolamine; diethanolamine; triethanolamine; monoisopropanolamine; diisopropanolamine, and mixtures thereof. Preferably, the curing agent comprises 1,4-butanediol.
In an alternative embodiment, the UV absorber comprises poly-(oxy-1,2-ethanediyl)-xcex1-(3-(3-(2H-benzotriazol-2-yl)-5-( 1,1-dimethylethyl)-4-hydroxyphenyl)-1-oxopropyl)-xcfx89-hydroxy; 2-(2H-benzotriazol-2-yl)-4,6-bis-(1,1-dimethylpropyl)-phenol; dimethyl succinate polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol; bis-(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate; bis-(2,2,6,6-tetramethyl-4-piperidinyl)sebacate; and mixtures thereof. Preferably, the UV absorber is 2-(2H-benzotriazol-2-yl)-4,6-bis-(1,1-dimethylpropyl)-phenol.
The core may include a center and an outer core layer and the cover may include at least one inner cover layer. Alternatively, the golf ball includes a layer of tensioned elastomer material disposed between the cover and the core. In one embodiment, core includes a fluid filled, solid or hollow center.